General Speaker problems

hi, everybody.
My car is 91 toyota, corolla DX. My 5.25" speakers are broken, so i want to buy a new one.
But i found some problem about buying a new pair of speakers.

1.) What is coaxial speaker?? What is the difference??
2.) I found that the sockets of my old speakers are different to other speakers' sockets. so, do i need to buy something which can connect my old wire to the new speakers??
3.) Is 3-ways speakers always better than 2-ways speakers?? I want to change my rear speakers. Which one is better??
4.) will you guys buy the speakers at Best Buy?? I found that if i get one on e-bay, the price is related cheaper.